1. Field of Invention
The present invention relates to a microfluidic inkjet control method, especially a microfluidic inkjet control method that is used to adjust the inkjet waveforms of the thermal print heads.
2. Related Art
Inkjet printing technology uses precision element printing that is applicable to many different materials. It satisfies electronic industry's precision element production demands of automation, is more compact, has lower costs, has a faster production time and reduces the impact on the environment. For example: application on the color filters on the liquid crystal display panel and the organic polymer light emitter diode, PLED, production. The color filter is composed of red, green and blue colors, spread on the substrate and also the black matrixes between the color ink. The inkjet printing process is to spread the ink droplets directly on the concavities formed by the black matrixes on the color filter substrate. Different types of color filters have different color spreading patterns. Compared to the semiconductor production method for color filters, the inkjet printing equipments and production costs are dramatically decreased. The inkjet production method for the organic PLED is similar to the described color filter production method, the only difference is: the organic PLED does not need the black matrixes structure. The organic light emitting material build photo-resistor banksto separate and guide the flow of different material colors.
However, the generic inkjet production method for color filters or organic PLED has a major problem caused by the satellite ink droplets that accompany the main ink droplets. If the satellite droplets are formed as ink drops break off during the drop ejection, it will follows the main drop to land on substrate, and typically, has position deviation with main drop, then makes a defect on substrate. This characteristic occurs randomly. The path of the satellite droplets usually has a slightly different angle shifted from the main ink droplets and has scattering distribution. This behavior causes serious problems, such as color mixing and low performance efficiency. At the worse case scenario, the satellite droplets can be as far away from the main droplet as 100 μm. For the stripe color filter or organic PLED, the satellite droplets have less influence in the horizontal direction, but would cause color mixing in the vertical direction. If the distance between the nozzle and the printing substrate is large, the satellite droplets can fall further away from the main droplets. The simplest solution is to move the nozzle closer to the printing substrate, so the satellite droplets are hidden within the main droplet. However, if the nozzle is too close to the printing substrate, it is easy to scratch the substrate. On the other hand, if the distance is too short, the ink drops may not be able to break-off completely, so they are dragged on the substrate; this can cause the main droplets to be shifted from the predetermined position and color mixing.
The method for solving the satellite droplet problem completely is to reduce the probability of their occurrences. Since the density of ink increases as it is heated, the size of the ink droplet becomes inconsistent, and it may even influence the deviation straightness of the ink and make the satellite droplets problem worse. Therefore, the internal flow structure of the print head needs consist with the characteristics of the ink (viscosity coefficient and surface tension) and the surface characteristics of the nozzle material, or by changing the driving waveform of the nozzle to reduce the occurrence of the satellite drops by controlling the ink ejection condition. Such as the inkjet driving method proposed by U.S. Pat. No. 6,331,039, which divides the driving signal into two stages. The first driving signal preheats the ink and does not eject the ink. After a rest period, the second driving signal then ejects the ink. By using the first driving signal and the rest period, the ink ejection amount variation, which is changed with differential outside temperature, has been controlled.
As described in U.S. Pat. No. 6,357,846, when the nozzle is idle for a period of time, the viscosity of the ink in the nozzle near nozzle opening increases and causes the ejection of the ink drop to be unstable. The patent revealed a method to adjust the ink ejecting waveforms by adding a fine vibration to the main driving waveform. Using the fine vibration to provide the ink viscosity energy can keep the ink in a more consistent uniform condition. Input signals control the two kinds of waveforms to reduce the problem caused by the increasing viscosity of the ink droplet. The method must use two signals to control the main driving waveform and the fine vibrating waveform separately, so it is more complicated.
Since the ink droplet's ejection amount during the inkjet process is easily affected by the change in ink cartridge pressure and the environmental temperature, which affect the element's homogeneity, a more appropriate ink ejecting signal can be provided by adjusting the ink ejecting waveform or changing the driving method of the print head. As described in U.S. Pat. No. 5,798,772, modulating the pulse width can provide different heating energy. The heating energy and the voltage ratio are kept constant to improve the image quality. U.S. Pat. No. 6,439,687 provided a printing head driving method that changes the regular block driving. By using an irregular block driving sequence method it reduces the pressure variation affecting the ink cartridge, increasing the quality of the image.
Also, using the inkjet method to produce components requires very precise positioning to eject the ink droplet onto a predetermined position. Since the inkjet procedure of every type of color filter or organic PLED requires different resolutions and different types of components, they require complicated control systems and adjustment mechanics. These cause device pixel with different types or resolutions, requiring specific production equipments or printing head designs. Therefore, an efficient and simple control method to complete different types of components during the inkjet production process is a major development goal of the inkjet production technique. Like the inkjet alignment correction apparatus for color filter production described in U.S. Pat. No. 5,984,470, the to be printed color filter and the nozzle of the print head has displacements. Further, the apparatus adjusts the nozzle angle to the to be printed color filter substrate to execute inkjet printing to the color filter with the correct resolution.
However, the described print head driving method or the waveform adjustments are focused on the different specific problems and it is easy to create problems while fixing another, so an inkjet production control method needs to provide overall improvement.